Recording oscillograph



Dec. 20, 1960 G. w. DOWNS RECORDING oscILLoGRAPH 3 Sheets-Sheet l FiledApril l, 1957 iNvENTOR. GEORGE W, Dow/v5 A TTok/VEY 3 Sheets-Shee'. 2

G. W. DOWNS RECORDING OSCILLOGRAPH INVENTOR.

GEORGE M Daw/vs BY /P Dec. 20, 196D Filed April 1, 1957 A T roRNE Y Dec.20, 1960 G. w. DowNs RECORDING oscILLoGRAPH 5 Sheets-Sheet 3 Filed Aprill, 1957 INVENTOR. GEORGE W. Dow/vs BY Y A Tron/VE Y rlte StatesP211tCliff@f RECORDING OSCILLOGRAPH George W. Downs, Altadena, Calif.,assignor, by mesne assignments, to Consolidated ElectrodynamicsCorporation, Pasadena, Calif., a corporation of California Filed Apr. 1,1957, ser. No. 649,709

s claims. (ci. 346-110) This invention relates to improvements inOscilloscopes and particularly to osciloscopes in which oscillographtraces are of more nearly uniform contrast relative to the backgroundagainst which the traces appear.

Oscilloscopes are generally of two types. In one, an oscillograph traceis displayed visually but for only a relatively short time on a screen,usually for not more than a few minutes. Cathode ray tube Oscilloscopesof this type are well known. Usually in such an arrangement the trace isproduced by repeatedly moving the beam at scanning speed along atime-axis and simultaneously deflecting the beam in a direction aboutperpendicular to the time-axis by amounts that vary with the amplitudeof the signal under investigation. In another type of oscilloscope, morecommonly called an oscillograph, the trace is recorded permanentlyjonphotographic paper or other recording mediumV in visible form. In eithertype of oscilloscope the tracemay be in the form of a. brighttraceagainst Aa dark background, or it may'bein the form of a dark traceimpressed on av light or-bright background.

.In the particular oscilloscope to which the invention has been appliedas described hereinafter, an electron beam projected toward a screen ofa cathode ray tube is deflected only along a specic deection axis inaccordance with the amplitude of applied signals, and the image of thebright spot produced on the screen is projected to an image positionpast which recording photographic paper is moved-at a constant speedalong a time axis. With such an oscilloscope, an oscillogram is producedin which the signal is recorded as a variable deection as a function oftime.

Oscilloscopes are employed to display traces which are characterized bywidely different frequencies and widely different amplitudes. The speedof the electron beam or other spot which produces the trace depends onboth the instantaneous amplitude and the frequency of the signal beingrecorded. It also depends on the scanning speed of the electron beam ofthe cathode ray oscilloscope or of the recording paper as the case maybe. As a result, the intensity of a trace, or more broadly its contrastwith the background, varies from point to point along the trace, andalso varies from trace to trace when different traces have differentamplitude or frequency characteristics. The lack of uniformity of thetrace sometimes results in serious loss of information respecting thesignal that is recorded.

More particularly, if the intensity of the spot is suitable for use withvery low frequencies or very low amplitudes, -then when the speed of thespot is high compared with the scanning speed, the display or record ofthe trace may be very feeble or even completely absent. As an example,when employing a cathode ray oscilloscope, the normal potentials of thecontrol elements are adjusted to' such a value that the beam does notburn out or otherwise injure the screen at any point where the beam mayremain at rest while no signals are applied. Subsequently when agsignalis appliedthebeam then moves across the face of the screen at aninstantaneous speed that depends upon both the frequency of the signaland the instantaneous amplitude of the signal.

In such a case, when a sine wave is applied to the beam, and thescanning speed is low, the speed of the beam is a minimum at the peaksof the sine wave and is a max mum at the points where the sine waveintersects the time axis, that is, at the instants halfway betweensuccessive wave peaks. Consequently when a sine-wave signal isreproduced as as oscillograph trace, the contrast is greater at thepeaks than elsewhere and is least at the points midway between thepeaks. Similarly, when a transient pulse having a short rise-time orshort falltime is reproduced, the sharp parts of the pulse at the frontor tail ends are weak and, in fact, often invisible.

The foregoing difficulties are encountered not only when employing acathode ray oscilloscope for displaying a signal and not only whenemploying a cathode ray oscilloscope for producing a photographicoscillograph trace, but even when a galvanometer carrying a deliectionmirror is employed to produce a trace in an ordinary photographicrecording oscillograph. Even though sucn diculties are present in othercases, the invention will be described particularly hereinafter withreference to a specific type of recording oscillograph in which thesource of light which produces the oscillograph trace is a moving br.ghtspot on the face of a cathode ray oscilloscope.

Accordingly the principal object of this invention is to provide animproved oscilloscope with which an oscillograph trace characterized bymore uniform contrast can be produced.

Another object of the invention is to provide ksuch an improvedoscilloscope which utilizes auxiliary parts which are few in number andwhich increase the cost of the oscilloscope very little.

Another object of the invention is to provide such an improvedosci.loscope which is capable of being used over a wide range ofamplitudes and a wide range of frequencies.

The foregoing and other objects and advantages of the invention willappear more fully from a consideration of the descnption of oneembodiment of the invention which follows. Although only one specificembodiment of the invention is illustrated in the accompanying drawingand is described herein in detail, it is to be expressly understood thatthe drawing and the descript on are illustrative only and that theinvention is not limited thereto, but that the invention may be embodiedin many other forms within the scope of the appended claims.

In the drawings:

Fig. 1 is a schematic dagram of a recording oscillograph embodying myinvention;

Fig. 2 is a detailed wiring diagram of the circuit of Fig. 1;

Fig. 3 is a series of graphs employed to explain the operation of theinvention; and

Fig. 4 is a schematic diagram of a modification of the oscillograph ofFig. 1.

Referring to the drawing, and particularly to Fig. 1, there isillustrated an oscilloscope in the form of a multiple trace recordingoscillograph. This oscillograph is of the general type described andclaimed in Patent Number 2,614,460 which issued to William MillerInstruments, Inc. on October l2, 1952. In the oscillograph illustratedin Fig. 1, signals from each of a plurality of sources S are impressedupon a pair of electrostatic deflection 'plates P of a cathode rayoscilloscope tube CRT. In practice the signal from each source S isamplified by a push-pull amplifier A having a low output impedance priorto application to the deflection plates. The ampliiied signals. thuscause an electron beam B to-be deilected along a straight line on theinner surface of the face of the cathodev ray tube. In eiect the beam isdeflected along a deection axis Y in a vertical or ordinate direction,and since. in this case no other deecting forces are applied to thebeam, there is no. cletlection of the beam along the time, or X', axisin a horizontal or abscissae direction.

Each of the cathode ray tubes CRT is of a type in which the part of thescreen C` struck by the beam B; fluoresces or otherwise emits radiationwhile the beam is striking that part. In this embodiment of theinvention a P11 or P4 phosphor is employed. In this casey therefore, thescreen is of thev uorefscent type in. which there is substantially no:persistence. Consequently the screen radiates a; smalslcrsplot of lightwhich travelsfwith the electron beam. B. alorg. the deetien axis. Ysimultaneously with the. movement of the electron beam B, across thescreen. cathode. rayr tube which has provedl to b e satisfactoryv for mypurposes is a tube bearing the typey number 3ABP11. Such `a screen emitslight having high actinc qualities while the. electron beam is impingingthereon arid'thC illumination from any spot diminishes rapidly when thebeam moves from that spot. In effect the luminous spot moving up anddown along the line Y is a moving source of light of nearly con-tantintensity.

An image of the cathode ray tube screen C is projected by means of anvoptical system, here represented simply by the lens L, 'toy a recordingzone. 4Z past which a strip Ry of. recording photographic p^per- Vismoved. An image IV of the moving source O is thus moved along an axis Ywhich is the conjugater imagein the recording zone of the axis Y on thescreen. The recordlngpaper R is moved at' constant speedfn a.,direction.perpendicular.

to the image axis Y', thus causing anoscilllograph trace;l

W of the signal fromtvthe. source S tol bereeorded on the recordingpaper; .The cathode ray tubesv C RT and the;

The.. present. invntipn relates. partit:u larlyV to an.

movement' which makes. it. possible t9. Profiuse. @Scilloa graph traesonl the recordingpaper`- R whichare of, more.y nearlyY uniform intensityr. contrast than4 has-heretofore.,

been obtained.v In some oscillograms a. dark or black trace is recordedagainjt a gray orA white background.

In others a bright oi'` w1-ite trace is recorded. against a black orgray background. In either casefgreaterw contrast exists on the trace atthe peaksv p and less. contrast occurs elsewhereon the trace., Inoscillograrnst produced heretofore the. Contrast at the peaks. of thesignals have been relatively great while the contrast of parts off` thewave between the peakshave been relatively weak sometimes not appearingat all. The reason for thisobjecg tionable phenomenon has longbeenwellkpQWn'-,

In the present embodiment of the inveiitiorl,` ll'lightv spot O isbright againstthedarkbackgroundgof the screen C while.. the. recordedtraces W aren blackV against the. neutral or light grey background ofltheunexposed par-tl of the recordingpapen. The portions ofthe'waveatgthepeaks p are dark because the photographic exposure isgreater there than at` intervening points,` and the, portions.-y

of the waves at. theifintervening positions' mare lighter.-

becausethenegtjposnre there .is lessi InA the oscilloscope.

illustratedfin Eig. 1 itrisV-cleai-,that the I exposure is greater-f atther peaks. than at theintervening pointsV and isf less. at theintenvening points than at they peaks, because; the velocity of travelofthetspotO on thev screen iszeroE at'the; peaks and; i,s;high y at;intervening positions.;A

The amplitude of a sine wave is given by the following formula: y=a sinwz (1) where y=deliection of the spot along the line Y from its normalor zero position;

a=amplitude of the wave;

#frequency Qt the wave; and

t.=time. l

Furthermore the speed of travel of the s-pot O on the screen C is, givenbythe equation S=aw, cos wz If the intensity of the electron beam B isconstant, which it normally is in all prior cathode ray oscillo-`scopes, the apparent brightness or intensity of the spot O in terms of'total luminous energy per unit area` is lar-ge when thespeed of the beamor spot is zero and also when the beam dwells at a spot f or only ashort time compared with the persistence time of vision. ButI on theotier hand, when the intensity of the electron beam B is contant, the,total luminous energy per unit area or apparent brightnessA is low whenthe speed of the beam is high. It is to be noted that the spot speed Sis proportional to the amplitude of the wave and also to the frequencyof the wave. The apparent brightness is thus4 a function of the timeintegral of the low brightness. This accounts for the variation instrength or contrast ofthe trace from spot to spot and for the wellknown fact that certain parts ofrecorded oscillograms are normally moredifcu't to see than others.

The exposure of the photographic paper R depends not; only on the speedof` the light. spot O along a detiection axis Y but also onV thescanning speed of the. paper.. Thel total effective speed of theVspot'is the speedrelative" tothe paper itself; This speed is; determinedby the vector sum of the spot speed along the axis Y and' the scanningspeed along the' time axis. In a. similar way, in an ordinaryoscilloscope employed for visual display' of a trace on a screen C', thespeedof the spot on the screen is determined by the vector sum of thespot deflection velocity andk thefscanning velocity. In practice the,range of contrast obtained depends on therange of total; spot speedasthus determined vectorally. Signifif cant and' substantial differencesin contrast occur'l whereg,y the spot deflection speed is'largecompared'with tllesggaitfl ning-speed'.

ln accordance with this invention, differences in tracem contrast arereduced oreven substantially eliminated by varying the intensity of thebeam B and hence the n.- tensity-o-f thesource oflighrO'as a functionof-'the'speedy soY that the various parts ofv the' trace are recordedwith; more-nearlyvequal-lmexposure'. With this invention the apparentintensity of the spot O ismade more'nearlyA constantaregardlessotthe'amount o-f deflectiony of'fthespotand" regardless of thefrequencyofthe signal'. For'thesame reason, the exposure ofl thephotographic paper is: more nearly constant at" all times; so4 that theZvarious parts ofthe recorded traceare of more nearlyuniform*- contrast.V

In accordancewith this invention; the signal'from each' sourceS isyimpressed upon anintensitycontrol unit-ICU which is employed to vary theintensity of-the-electron beam B and-hence the intensity of'vthe spotO.Thev in: tensitytof'the spot Or is soxvaried as. to producegreateruniformity'I ofithefapparentintensity of thespot O, greateruniformityain theexposure of the photographic paper R, andhencev-greaterf-uniformity-inthe lcontr-ast offthe trace T; Since all'Irecordingfchannels-operate in -the'same-:waygI onlyone willlberd'escribed-i As shownin greaterdetail in- Fig; 2, eachfintensitylcontrol unit ICUtincludes acombinationofditferentiatorVcircuitsD'andffullwave rectiiier-y F andlae storage orkde-vmQdulatorfcircuit M: With thisgunit .[CU the amplified?.v

signal is differentiated and then fully rectified. The rectilied signalis then impressed upon the storage circuit M.- And the output of thestorage circuit is employed to control the intensity of the beam B.

At frequencies that are very low, the intensity of the beam B is variedinstantaneously, but by only a small amount. of the beam is increased bya large amount to a substantially fixed value that depends on theamplitude of the signal but is independent of the beam speed. Atintermediate frequencies the intensity of the beam B is of normal valuewhen the speed of deection of the spot is zero and is increased when thespeed of detlectionis increased. A time delay circuit TDC in the form ofa low-pass filter is employed in the path between amplifier A and theplates P. This circuit delays the application o f the high frequencysignals to the deliecting plates P until the intensity of the beam B hasbeen raised.

The signal amplifier A is of the push-pull type, having a groundedcenter tap to and output terminals 11 respectively. Two resistors r1 andr3 are connected in series between each output terminal t1 and one inputterminal 13 of the time delay circuit TDC. The output terminals t3 ofthe time delay circuit TDC are connected to the two deflection plates Prespectively.

The electron beam B is energized by means of a potential applied from asuitable power supply PS. A potentiometer p1 is included in the powersupply PS. The positive end of this potentiometer is connected directlyto the cathode K of the cathode ray tube. The control grid CG of thecathode ray tube CRT is connected through a. resistor R2 to a slidingcontact s3 of a potentiometer p3. The negative end of this potentiometerp3 is connected through a resistor R1 through the sliding contact s1 ofthe first-mentioned potentiometer p1. The base or normal intensity ofthe beam B is established by adjustment of. theslide s1 of thepotentiometer p1. The base or normal beam intensity is established at alevel such that there is little inclination of the screen C of the tubeto burn out or otherwise become permanently injured when no signal isapplied to the deflection plates P.

A balanced pair of differentiator networks D is connected across theoutput of the amplifier A. Each of the differentiator networks includesa dilerentiating capacitor C3 and a differentiating resistor R3. The tworesistors R3 are connected in series between the two condensers C3 andthey are coupled to the output of the push-pull amplifier A byconnection of the condensers C3 to the junctions between the resistorsr1 and r3 in the signal line. Two diodes H are connected face to face inparallel with the two resistors R3, the negative terminals or poles ofthe diodes being connected together.

Thus the resistors R and the diodes H form a full-wave.

rectifier F. The potentiometer p3 is connected across the output of thefull-wave rectifier F with the junction' between the resistors R3connected to the negative end of potentiometer p3 and to the slidingcontact s1 through the resistor R1. Two condensers C4 and C5l areconnected in series across the potentiometer p3. The junction betweenthe two capacitors C4 and C5 is connected to the slider s3 through theresistor R1 and also to the control grid CG. The potentiometer p3,resistor R3 and the capacitors C1 and C5 form the storage circuit Mwhich includes an input circuit connected across the output of thefull-wave rectifier F and an output circuit'which is formed across thecapacitor C5 andconnected between vthe control grid CG and the resistorR1.

Generally speaking, the output of the full-wave rectifier F is appliedacross the potentiometer p3 and a fraction of this voltage is appliedtothe control grid CG in accordancewith the position of 4the slide s3.Because of, thelnature o f the connections, the voltage of the com trolgrid CG is driven ina positive direction relative to its normal valuewhenever.l a signal is applied to the amplier. causing the intensityptthe eleetwabeam At frequencies that are very high, the intensity B tojbeincreased and thus `causing the intensity of thI spot O to be increasedcompared with the normal values.

that the intensity .of the beam and the intensity of the spot would havein the absence of the intensity control unit ICU. Thus it is seen thatthe intensity of the spot O is increased whenever the deflection speedof the spot across the screen is increased.`

The action of the intensity control circuit can best be understood byseparately considering the action at different frequencies. f

Consider now the action of the intensity control unit when a relativelylow frequency sinusoidal wave is ap plied from a signal source S. Itwill be noted that the signal impressed upon the intensity control unitICU is af sine wave W1 as indicated in Fig. 3. The difieren tiatingnetwork produces a signal across the resistors R3 which is a cosinewave'Wz. The cosine wave W3. is the derivative of the sine wave W1. Therectiers H produce across the output of the fullswave rectifier F asequence of half-wave pulses represented by the wave W3. These pulsesare all of the same polarity but are otherwise in phase with the cosinewave W3'. It will beA noted that the rectified wave W3 has a series ofcusps of zero value at the instants when the wave W1 reaches its peakvalue. For this reason the intensity of the beam B is its normal valuewhen the speed of the spot O on the screen is zero, that is when thepeaks of the waves are being reproduced. Likewise it will be noted thatthe half-wave'pulses of the rectied wave W3 attafn their maximum valueswhen the sine'wave W1 has a zero value. For this reason the electronbeam B has a maximum intensity when the speed of the spot O is a maximumwhen the portions of the wave between the peaks p are being recorded.

The action just described occurs substantiallyas *de*- scribed when theperiod ofthe signal is very low cornpared with the reciprocal of thetime constant of each of the differentiating networks D. At v ery highfrequencies differentiation does not occur, since the capaci-- y' F thuscausing the intensity of the beam B to be raised to a higher value thannormal throughout the entire period o-f application of successive pulseso-f the signal wave W1.

At high frequencies the two capacitors C1 and C5 divide the voltageappearing at the output of the rectier F. Accordingly at the inceptionof a transient, the bias impressed upon the control grid CG changes at ahigh rate, thus increasing the intensity of the beam atf This makes itpossible to record distinctlyaA high rate. the short-rise portions ofsuddenly changing signals.

If only waves having frequencies of an int;rmediate frequency aresupplied from the signal source S, a wave W5 having a form intermediatebetween those of the waves W3 and W4 appears across the potentiometer-pz In this wave W5 the 4cusps do not reach zero, so thatin effect aliuctuating D.C. voltage is impressed between,

the control grid CG and the cathode K.

Due to the action of the differentiators D the amplitude of the signal.appearing across the resistors R3 'is small, the amplitude of the waveW5 is of intermediatevalue, and the amplitude of the wave W4 is large.'Ihusg4 the average bias provided by the intensity control unitA ICUincreases with the frequency of the signals, thus having an effect whichincreases with frequency even `reason the effectiveness of theintensity' control unit in creases with neejd'aY Some time elapsesbefore the` voltage across the output' ofthe rectifier attains itsstationary pulsating or sawf-'tooth' character as: indicated by the'shapesof the waves W3, Ws and W5. Thistimeconstant is determinedY verylargely by the resistance of' the potentiometerv pg' andthe values ofthe capacitanc'esx of the capacitors C4 and C5. In order to make itpossible to record a` trace ofY high contrast at high frequencies, atime` delaycircuit TDC is employed which is characteried by a time delayabout equal to the time constant of the demodulator ncircuit, M. Thetime delaycircuit may be4 aseries of loWt-s pass filtersl havingcut-off;l frequencies; each of which' is about equal to twice the`highest' fre'quenc'y'o' the signals to bei reproduced; TheI timeKdelaycircuit TDC mayl also of coursel be in thejform' o' anl allf-passcircuit, that" is, a time delay circuit having substantially' uniformattenuation: Such time delay circuits are well known in^ the art andneed not be described here.

Itis not" necessaryl for diiferentationto occur throughout the entireband of frequencies ofthel signals that are: to be reproduced. Thereason forV tl'lis is that perfect' correction of contrastby` perfectcontrol of' apparent spot intensity to overcome effects due' tovariations of beam speed is not required. Nevertheless the networks" Dare" called differentiators because normallyr they approxi matelydifferentiate over at least a` large partof the band: of" frequencies ofthe waves being reproduced. Nori mally/ the time constant of each' ofthel dfferentiator networksD is equal to aboutl the periodV of wavesnear themiddle ofthebandi of:` waves that' are toy be reproduced and thetime constants of` networks of" the' demodulator circuit are also butther same' as the time constant' of? each of' thedfferentiator networks;

Inany" event, while thedfferentiator is` operative, the intensityy of"the beam vB isvaried; in accordance with the: speed of the spot O, theintensity'Y increasing instantaneously with the speed oA the` spot and?decrea ing instantaneously with decrease in the speedv `of' the spot.But a't high frequencies, the intensity of the beam is increasedthroughouty a period that is longv compared withk theyperiods of thewaves;

Al typical setl of values whichl have: bren employed' successfully whenno time delay circuitTDC ha's'been employe'dare as' follows:

R3=l-50 kilohmsT r2 =33kilohms With these particular circuit constants,it-v will` be noted, the time constant of the storage circuit formed by`the capacitor`C5- and the lower portion` of the potentiometerv pa is:`longer than thel time constant of each of. the differentiator networksD'V exceptV when the? slider s2 is very near thel negative end of theApotentiometer" p2; Accordingly some storage action` occurs with thiscircuit even in thee rangeV of! frequencies in whch*` diferentiatio'noccurs'. Asa result-*the cuspsof?waveW- do not reach zero but" aretv inthe form of the vall'eysf of' wave 'Wg at al plateauabovel thezero-voltageelevell A circuit having; suchconstants has been employedsatisfattorily inim proving the recording vof"\\faves linafrequency'range` from 101c.p`:s. to 40,000:c.p.s;

IniA practiceathe: slider s1 isy placed"y in a'- positionwherer iarecordfhaving satisfactory contrast@ is' obtained= even withwavesofflowLfrequencyeandflowarnplitud and theslide'r" s2 iSset'n-afpositionin'whiclr satisfactorycontrast is-ob-'f tained with-waves of?high` frequency and high amplitude; Inotherwords; in effect,the-position'ofthe'sliders1 deterV mines-1hr contxastwlicni thefs'pot O`is. stationary-andi the position of the' slider' si deter'rnirresf thecontrast when the' spot-speed is high?. By setting" the potentiometer toprtA vide morenearly equalZ contrast at both high and low spot"lvspeeds, improvement is also obtained af intermediate spot speeds:Inanyfe'venr, even though enact; compensationy is notfachieved", theloss of signal whenlthe speed of the'spot' isv high is substantiallyeliminated; By employing the time delay circuit together withthevintensity'r control cir'-y cuit; verysatisfactory* contrast mayI beachieved` with` traces inboth high frequency* and low frequency regions.However, satisfactory results' have been obtainedl even' without theuse'of al time delay circuit.

' ReferringtoFig's'. 1 and 4; it is" to` be noted that the record paperR is driven by' means of a capstan J driven by aVv motor M` throughasolenoid-operated speed changer SCA and a solenoid-operated'clutch SCL.In practice, a's shown more clearly in* Fig. 4', the start-stop unit SSWis arranged in conventional manner to-raisek the bias appliedA to the`cathode ray tubev from a high value to a normal value byf closing' theswitch s ati theY sarne time that the solenoid-operated clutchl SCL isclosed; In this wayy the intensityofthebeanrislowwhen'no signal at allis beingj recorded andthe bias isincreased to anormal value that dependson the speed of the palper when a recording. isVV being made. For thispurpose aspeed'selector is also usedJ to' control bias; Y e n Y l Aspeed selector unit SSL is employed to operate the solenoid-operatedspeed changer SCA. This speed K changer is ofa conventional type inwhich the speed off the capstanl maybe selectively set atV a number ofpre-v determinedlvaluesfor'a given predetermined speed'of the motor Mi,The speed' selector-` unit SSL is arranged` to* COnnectdifferentsliders's", sf', slf" on the` potentiometer pf2 to the` resistor R11 `soasto establish the normal intensity,i

= of the' beam Bjat a'dilerent value in accordance with thet andhencethe intensityofv the spotOis relatively'l'ow; and:

forhig'h paper speeds; the intensity ofthe beam B` and they spot O.isrelatively high. In this way" compensation for paper speed' may beachieved, producing more" nearly@ equal exposure ofthe photographicpaper regardless of" thepaper speed'.

The desired change in bias voltage with change'of ,spe'ed isV achievedby means of' normally" open' switches Q1, Q2; and" Q3 that are*connected between the respective sliders si', si, and's'l" and theresistor R1. These switches are operated by'a control lever of the speedselector unit-SSL,

so'that one'or another'is closed ata time, dependingupon thespeed ofithepaper; SSL is adaptedto close one orV another of three normallyopenswitcheslQl, Q5 and Q6 in order t'o connectV one orl auf' other'of threesliders'sz', sj" and szf" of theA potentiometerA p2; It' is' to benotedthatth'esliders'sz, s2" and sgf are' arranged to applyl a" smallerfraction ofV the voltage tov the control grid CG when the speed of thepaper is in-v creased. In practiceliowever, itisA found that the systemi may" bell operatedv quite' satisfactorily' without employin'gfthe'latter set ofs'witches'. Butwhen they are employed',4 these switchesQ4, Q5 and Q8 are ganged with the switchesl Q1, Q2 andQJ so" that oneswitch in each of the circuits isclosed, dependingu'pon thev7 speed ofthe paper;

While the invention 'has beenA described withl particular reference toAasysten-r v inwhich the electron' beam' Bv is the correspondingspotsfreco'rded' on a moving strip-of photor'grapiii'c'Y paper, it willbeuntiers'toodl that the inven# 761i tiomi'szalsolapplicableto e asystemin which thefbeam isf Similarly, the speed selector unil:

`periodically oetiected along a time axis of the cathode ray tube whilebeirg deflected along the deflection axis. Since various means forproducing such periodic deflection of the beam along a time axis arewell known to those skilled in the art, they are not described here.Suffice it to say, though, that in such a case, a second pair ofdeflecting plates is employed and a saw-tooth wave or other deflectingsignal is applied to this pair of plates in a conventional manner todeflect the beam in a direction transverse to the iaxis Y.

It is thus seen that I have provided an improved oscilloscope in whichoscillograph traces of more uniform contrast can be produced. Though theinvention has been described with referencev to only one specificembodiment thereof, it will now be understood by those skilled in theart that the invention may be embodied in many other forms withoutdeparting from the scope of the invention. It will therefore beunderstood that many changes may be made therein, such as changes in thenature of the light source, changes in the nature of the recordingmedium, and changes in the type of traces produced, and that manychanges may also be made in the circuits and other specific elements,without departing from the invention as dened by the following claims.

I claim:

1. In an oscilloscope in which an oscillograph trace of variabledeflection is produced on a strip of recording medium:

means for generating an electron beam and for projecting said beam ontoa screen to produce a spot thereon;

a signal source;

means for applying deflection forces to said beam to dellect said spotalong an axis on said screen in accordance with signals from saidsource;

means for moving a strip of recording medium past a recording zone;

means for projecting an image of said spot onto said recording zonewhereby an oscillograph trace is recorded on said strip, the contrast ofsaid trace at any one point relative to the background on said stripdepending upon the speed of deflection of said spot along said axis ofsaid screen, upon the intensity of said beam, and upon the scanningspeed of said strip;

means for selectively setting the speed of said strip at a relativelyhigh value and at a relatively low value and for simultaneouslyselectively setting the intensity of said electron beam at a relativelyhigh value and at a relatively low value, said low value being ofsufficient intensity to cause the electron beam to produce a spotcapable of being recorded on said strip; and

additional means controlled by said signals for varying the intensity ofsaid beam as a function of the spot deflection speed whereby changes incontrast of said trace on said strip that would otherwise occur when thebeam deflection speed changes are reduced.

2. In an oscilloscope in which an oscillograph trace of variabledeflection is produced on a strip of recording medium:

means for generating an electron beam and for projecting said beam ontoa screen to produce a spot thereon;

a signal source;

means for applying deflection forces to said beam to deflect said spotalong an axis on said screen in accordance with signals from saidsource;

means for moving a strip of recording medium past a recording zone;

means for projecting an image of said spot onto said recording zonewhereby an oscillograph trace is recorded on said strip, the contrast ofsaid trace at any one point relative to the background on said stripdepending upon the speed of deflection of said spot along said axis ofsaid screen, upon the intensity of said beam, and upon the scanningspeed of said strip;

means for selectively setting the speed of said strip at a relativelyhigh value and at a relatively low value and t'or simultaneouslyselectively setting the intensity of said electron beam 'at a relativelyhigh value and at a relatively low value, said low value being ofsuicie'nt intensity to cause the electron beam to produce a spot capableof being recorded on said strip; and

separate means controlled by said signals for increasing the intensityof said beam above a normal value when the spot is being deflectedwhereby changes in contrast of said trace on said strip that wouldotherwise occur when the beam is being deflected are reduced.

3. In an oscilloscope in which an oscillograph trace of variabledeflection is produced on a strip of recording medium:

means for generating an electron beam and for projecting said beam intoa screen to produce a spot thereon;

a signal source;

means for applying deflection forces to said beam to deflect said spotalong an axis on said screen in accordance with signals from saidsource;

means for moving a strip of recording medium past a recording zone;

means for projecting an image of said spot onto said recording zonewhereby an oscillograph trace is recorded on said strip, the contrast ofsaid trace at any one point relative to the background on said stripdepending upon the speed of detlection of said spot along said axis ofsaid screen, upon the intensity of said beam, and upon the scanningspeed of said strip;

means for selectively setting the speed of said strip at a relativelyhigh value and at a relatively low value and for simultaneouslyselectively setting the intensity of said electron beam at a relativelyhigh value and at al relatively low value, said low value being ofsufficient in'- tensity to cause the electron beam to produce a' spotcapable of being recorded on said strip; and

means inc'uding a diterentiator connected to said source and a full waverectifier controlled by said differentiator for varying the intensity ofsaid beam as a direct function of the spot deflection speed.

4. In an oscilloscope in which an oscillograph trace of variabledeflection is produced on a strip of` recording medium:

means for generating an electron beam and for projecting said beam ontoa luminescent screen to produce a spot thereon;

a signal source;

means for applying deflection forces to said beam to deflect said spotalong an axis on said screen in accordance with signals from saidsource;

means for moving a strip of recording medium past a recording zone;

means for projecting an image of said spot onto said recording zonewhereby an oscillograph trace is recorded on said strip, the contrast ofsaid trace at any one point relative to the background on said stripdepending upon the'intensity of said beam and upon the scanning speed ofsaid strip;

means for selectively setting the speed of said strip at a relativelyhigh value and at a relatively low value and for simultaneouslyselectively setting the intensity of said electron beam at a relativelyhigh value and at a relatively low value, said low value being ofsufficient intensity to cause the electron beam to produce a spotcapable of being recorded on said strip; and

separate means including a demodulator circuit controlled by saidsignals for increasing the intensity of said beam when a signal ispresent whereby loss of contrast of said trace on said strip is reduced.

5. A beam intensifier circuit for a cathode ray tube comprising acathode ray tube including means for projecting an electron beam and acontrol electrode for vary ing the intensity of the beam, a signalsource, beam deflection means for applying dellection forces to the beamto deflect the beam in accordance with the signals from the source,rectifying means, having an input and au out putt'diiferentating meansVcoupled between the: input'v o f. the: rec'tifying means and the signalsource for differentiatingfs'ignal's having relatively low frequencies,a storage circuitv having. an input and an output, the input of thestorage circuit being connected across` the outputv oiv the rectifying.rmeans; direct current conductiveY means coupledv between the output ofthe1 storage circuit and the control grid of the cathode ray tube, thestorage circuit being arranged to provide a uctuating direct currentvoltage across the output in response to signals from the signal source*having relatively high frequencies, the average value of the.fluctuating direct current being proportional to the amplitude of thesignal, whereby at relative= ly low frequency signalsY ai voltageproportional to the derivative of the: signals is applied to the controlelec.- trode to increase the intensity of the beam. when itis beingdeflected and at relativelyy high frequency signals a fluctuating directcurrent voltage proportional to the am plitude of the signals isiapplied to the control grid to provide a high intensity beam for theduration of the high frequency signals.

6. A beam. intensifier circuit for a cathode; ray tube comprising acathode ray tube including means for projecting an electron beam and acontrol` electrode for varying the intensity of the beam, a signalsource, beam deflection means for applying deflection forces to the beamto deflect the beam in accordance with signals from the source, afull-wave rectifier having an input and output, aV dificrentiatorconnecting the input of the rectifier to the. source, a storage circuitincluding a resistor connected across the output, of the rectifier and acapacitor coupled across at least a portion of the resistor, the storagecircuit being. arrangedv to provide a fluctuating direct current voltageacross the capacitor in response to a high frequency signal beingapplied to the rectifier and direct current conductive means coupledbetween the capacitor and the control electrode whereby the intensity ofthe beam will be varied in accordance with the frequency and amplitudeof the signals from the source.

7. A circuit as defined in claim 6 wherein the storage circuit comprisesa potentiometer connected across the output of the rectifier and firstand second capacitors connected in series across the potentiometer, thepotentioml2 eter including a movable Contact, the junction of thecapacitors being coupled to the movable contact of the potentiometer,the direct current conductive means' being connected to the junction ofthe capacitors,

8. In an oscilloscope in which a visible oscillograph traceof variabledeliection is displayed on a screen; means for generating a variableintensity electron beam and for projecting said beam onto said screen toproduce such trace, the contrast of said trace at any point thereof relative to the background of the screen depending upon the speed of thedefiection of the beam relative to said screen and upon the intensity ofsaid beam; a signal source; beam defiection means for defiecting saidbeam from a reference position; an amplifier having an input forreceiving signals from said signal source and havingan output connectedto said beam deflection means for appying deflection forces to said beamto deflect said beam in accordance with signals from said source; afullwave rectifier having an input and an output; means including adifferentiator connected between the input of said rectifier and theoutput of said amplifier and a storage circuit having an input and anoutput, the input of said storage circuit being connected to the outputof said rectifier and the output of said storage circuit beingcoupled tothe means for generating said electron beam to vary the intensity of thebeam in accordance with the voltage developed across the output of thestorage circuit, the storage circuit being arranged to develop a directlcurrent fiuctuating voltage across the output thereof in response to ahigh frequency signal applied to said rectifier whereby the intensity ofsaid beam will vary as a function of the frequency and amplitude ofthe'signals from said source to thereby reduce the changes in contrastoccurring when the beam deection speed changes.

References Cited in the file of this patent UNITED STATES PATENTS2,448,771 Christaldi A- Sept. 7, 1948 2,700,741 Brown et al. Jan. 25,1955 2,726,918 Hathaway et al. ec. 13, 1955 2,828,357 Fyler et al. Mar.25, 1958 2,860,284 McKim Nov. 11, 1958

